The C. elegans tbx-2 gene encodes a conserved member of the T-box transcription factor family essential for development of ABa-derived pharyngeal muscles. The tbx-2 promoter is active in pharyngeal precursors prior to formation ofthe pharyngeal primordium, as well as in a subset of neurons and in body wall muscle in later embryos. We are examining regulation of the tbx-2 promoter to understand how pharyngeal muscle is specified in the ABa lineage. Based on results from a feeding RNAi screen of an expanded transcription factor library, I have found that tbx-2 promoter activity is repressed by the NF-Y CCAAT-binding complex and by TBX-2 autoregulatory activity. RNAi knockdown of either NF-Y components or TBX-2 results in strong ectopic expression of tbx-2 promoter::gfp in tissues that do not normally express tbx-2. I plan to pursue these observations by asking if NF-Y and TBX-2 repress endogenous tbx-2 expression, by identifying cis-elements in the tbx-2 promoter targeted by these factors, and by determining if NF-Y and TBX-2 repress tbx-2 expression in the embryo. To identify additional mechanisms regulating tbx-2 expression I am also characterizing a tbx-2 transcriptional enhancer that is necessary and sufficient for expression in the embryonic pharynx. My objective is to identify cis-acting sequences important for enhancer activity, and to identify and functionally characterize candidate regulators of tbx-2 expression that target these sequences. Finally, I will carry out an RNAi-based screen to identify transcription factors regulating tbx-2 as genetic enhancers of a weak tbx-2 mutant. Collectively these aims will elucidate the developmental pathway regulating tbx-2 expression and specifying ABa-derived pharyngeal muscle fate.